1. Field of the Invention
This invention relates to an image processing apparatus such as an apparatus for reducing a bi-level image or an image represented by two different levels, for example, black and white levels.
2. Description of the Prior Art
There are two general methods of reducing a bi-level image, that is, a simple thinning-out method and a decision-by-majority method. According to the simple thinning-out method, pixels of an original image which are spaced at predetermined equal intervals are selected as effective pixels for a reduction-resultant image, and the other pixels are ignored. According to the decision-by-majority method, an original image is divided into local areas, and the level of a pixel of a reduction-resultant image which corresponds to a local area in the original image is determined in accordance with the number of black pixels within the local area.
In the decision-by-majority method, a small black point and a thin black line in an original image tend to be omitted from a reduction-resultant image. Thus, the quality of a reduction-resultant image is low for an original image which has many small black points and thin black lines. Furthermore, in the decision-by-majority method, the density of black pixels in a reduction-resultant image tends to be higher than that in an original image, and a fine-pattern part of the original image may be inaccurately reduced.
Also in the simple thinning-out method, a small black point and a thin black line in an original image tend to be omitted from a reduction-resultant image.